1. Field of the Invention
This invention relates to a hydraulic actuator for shearing, drilling, bending or caulking a metallic workpiece or performing similar work on a metallic workpiece.
2. Description of the Related Art
As disclosed in Japanese Unexamined Patent Application Publication No. 58-224029, laid open on Dec. 26, 1983, there is proposed a portable and handy hydraulic actuator which comprises a pump block including pumps, and a piston having the front end fixed by a tool selected according to the work to be performed by the hydraulic actuator and operated by supplying operating oil by means of the pump. The pump block is a central member and a tool arm has a rear face which defines, together with the inner peripheral wall of the central member and the inner face of the pump block, a cylinder chamber in which the piston reciprocates. The tool arm is connected at a flange formed on its rear end to the central member at its front end by means of a number of bolts.
In this prior art hydraulic actuator, the number of bolts which connect the flange to the front end of the central member must be increased in order to withstand high pressure. This structure lowers the productivity of the hydraulic actuator due to the corresponding increase in manufacturing and assembling costs. When the bolts are tightened with uneven tightening torques or some bolts are not tightened well, the hydraulic actuator is likely to break under high pressure. For safe operation of the hydraulic actuator under high pressure, it is desired to provide a relief valve for returning operating oil to an oil reservoir when the pressure of the operating oil produced by the pump exceeds an allowable value, and an oil return valve for reducing the pressure exerted on the piston by rapidly returning the operating oil to the oil reservoir after the forward movement of the piston has started. However, the prior art hydraulic actuator having a thick flange through which a number of bolts are inserted does not have ample space for admitting these valves.